It is actually not possible to be allergic to histamine itself. But if you look up "histamine intolerance" on the internet you will come across a lot of bunk. A better term is "vasoactive amine sensitivity". It is thought to be do to a deficiency of the enzyme that degrades histamine and other biogenic amines in food in the gut. The enzyme is called DAO. If you have it, nothing will show up on any tests, and there is no reliable test for it, or DAO deficiency.

In my case, I am having severe reactions to foods with either histamine or biogenic amines. I don't have the symptoms if I stay off the foods (which is nearly impossible). The reactions happen within 30 minutes at which point I start to go into a vasodilation process, which triggers the pulsatile tinnitus and migraine. I also can get hives, rosacea, and diarrhea.

If I try to eat while on Pepcid, it's like eating dynamite (probably because if you block the H2 receptors it can increase histamine in the gut). My reactions are very intense and Allegra is not strong enough. Also, it alters my alertness -I have a job basically doing math all day.

I was not treated well at Mayo Allergy. They acted like they did not believe what I was saying and just making stuff up from the internet. It was a horrible experience. And they sent me home with intense, frightening symptoms and no place to go.